Enhanced LEDs Could Transform Lighting

Photonics.comJul 2004
TROY, N.Y., July 27 -- A research team at Rensselaer Polytechnic Institute (RPI) has developed a new type of reflector that dramatically improves LED (light-emitting diodes) luminance. The National Science Foundation (NSF) recently awarded the research team a three-year, $210,000 grant to move the patented omnidirectional reflector to market.
LED omnidirectional reflector developed by RPI researchers could brighten LEDs enough to replace the conventional light bulb. (Photo: Fred Schubert/RPI) "We have developed an omnidirectional reflector (ODR) for LEDs that will accelerate the replacement of conventional lighting used for a multitude of applications, such as lighting in homes, businesses, museums, airports and on streets," said Fred Schubert, an RPI professor who is heading the research effort. "The advance has implications ranging from major energy savings to contributing to a better environment and improving health."

LEDs are made from semiconductor "chips," the size of sand grains, covered with arrays of pencil-eraser size plastic bulbs. They are increasingly being used in traffic signals, automotive lighting and exit signs and have the potential to use far less electricity and last much longer than conventional fluorescent and incandescent bulbs. But current LEDs are not bright enough to replace most everyday uses of the standard light bulb.

"Only when the light generated is efficiently reflected inside the semiconductor can the brightness exceed that of standard lighting sources," Schubert said. "With the ODR, which reflects light at nearly 100 percent -- up to twice as much as previous reflectors -- we now have an LED that could revolutionize today’s standard lighting."

The ODR is a thin triple-layer coating that consists of a semiconductor, a dielectric material and a silver layer. Reports of the new reflector were published in a recent issue of the journal of Applied Physics Letters and in the Institute of Electrical and Electronics Engineers journal Electron Devices Letters.

In addition to NSF funding, the researchers also have received $250,000 in the last two years from the Defense Advanced Research Projects Agency to develop the new reflector.